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AP Biology Prokaryotic Gene Control Bacteria need to respond quickly to changes in their environment Transcription and translation happen simultaneously…they are “coupled!”  Transcription is what is regulated. Lack of nucleus makes this very efficient!

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AP Biology Prokaryotic Control of Metabolism Gene regulation  instead of blocking enzyme function, block transcription of genes for all enzymes in tryptophan pathway saves energy by not wasting it on unnecessary protein synthesis = inhibition - Now, that’s a good idea from a lowly bacterium! - -

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AP Biology Gene regulation in bacteria Cells vary amount of specific enzymes by regulating gene transcription  turn genes on or turn genes off turn genes OFF example if bacterium has enough tryptophan then it doesn’t need to make enzymes used to build tryptophan turn genes ON example if bacterium encounters new sugar (energy source), like lactose, then it needs to start making enzymes used to digest lactose STOP GO

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AP Biology Bacteria group genes together Operon  genes grouped together with related functions example: all enzymes in a metabolic pathway  Two types: INDUCIBLE and REPRESSIBLE Structures of an Operon  promoter = RNA polymerase binding site single promoter controls transcription of all genes in operon transcribed as one unit & a single mRNA is made  operator = DNA binding site of repressor protein

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AP Biology Operon summary Repressible operon  usually functions in anabolic pathways synthesizing end products  when end product is present in excess, cell allocates resources to other uses Inducible operon  usually functions in catabolic pathways, digesting nutrients to simpler molecules  produce enzymes only when nutrient is available cell avoids making proteins that have nothing to do, cell allocates resources to other uses